1. Field of the Invention
The invention relates to a shift controller (“shift control apparatus”) for an automatic transmission. More specifically, the invention relates to a shift controller for preventing shock during a shift of an automatic transmission from a drive range to a non-drive range, for example, when a garage shift is executed.
2. Description of the Related Art
Automatic transmissions installed in vehicles include multi-speed automatic transmissions and continuously variable automatic transmissions. A multi-speed automatic transmission is composed of a gear-type speed change mechanism and a fluid coupling such as a torque converter or the like. The fluid coupling serves to connect the multi-speed automatic transmission to an engine. The speed change mechanism may be a planetary gear-type deceleration mechanism for switching between a plurality of power transmission paths. For example, the multi-speed automatic transmission may be designed to automatically switch from one of the power transmission paths to another on the basis of accelerator opening and vehicle speed, that is, to automatically change the gear ratio (running speed stage). In the multi-speed automatic transmission, a new gear stage is established by engaging or releasing friction elements such as clutch elements, brake elements, and one-way clutch elements in a predetermined manner.
In general, a vehicle having an automatic transmission as described above is provided with a shift lever to be operated by a driver. Responsive to operation of the shift lever, a shift position (e.g., a reverse position, a neutral position, or a forward position) is set.
In order to move a vehicle from a garage for road travel or to put the vehicle into a garage after a trip, a shift from the parking (P) position to the reverse (R) position for moving the vehicle in reverse or a shift from a neutral (N) position to a forward (D) position or to the reverse (R) position, a so-called garage shift is made.
In making a garage shift, the automatic transmission is shifted from a drive position (the forward (D) position or the reverse (R) position) to a non-drive position (the neutral (N) position) in some cases, which creates various problems.
Japanese Patent Application Laid-Open No. HEI 10-61461 discloses a control apparatus for an automatic transmission of a vehicle which can prevent the vehicle from moving and enhance the durability of a frictional engagement device, irrespective of the rotational speed of a drive power source, in shifting from a drive (running) range to a non-drive range. This control apparatus controls the driving power source, the automatic transmission, and the shifting device. The drive power source is provided with an output increasing/reducing mechanism that is controlled by operating an accelerator pedal. The automatic transmission is connected to the output side of the drive power source through a hydraulically operated frictional engagement device disposed in a torque transmission path of the automatic transmission. The shifting device shifts the automatic transmission from a drive range to a non-drive range. When the automatic transmission is shifted from a drive range to a non-drive range by operation of the shifting device, the frictional engagement device is released so that the torque transmission path is disconnected. The control apparatus further comprises output control means. Before a predetermined period has elapsed after the shifting device has shifted the automatic transmission from a drive range to a non-drive range, the output control means suppresses increase in output from the output increasing/reducing mechanism even in the case where the accelerator pedal has been depressed to increase output from the drive power source. In use, this control apparatus for the automatic transmission, before the predetermined period has elapsed after the shifting device has completed the shift from a drive range to a non-drive range, the output increasing/reducing mechanism is restrained from increasing output and increase in the torque to be transmitted to the frictional engagement device is limited, even if the accelerator pedal is depressed to increase output from the drive power source.
Japanese Patent Application Laid-Open No. HEI 5-141284 discloses a control apparatus for a vehicular automatic transmission which suppresses the drag of a hydraulically operated frictional engagement device resulting from the movement of a shift lever from a drive range to a non-drive range, and which raises the RPM of an engine even if the shift lever has been shifted into a non-drive range. In this vehicular automatic transmission, if the shift lever is shifted from a drive range to a non-drive range, the hydraulically operated frictional engagement device that has been engaged is released, and a power transmission path of the transmission is disconnected. The control apparatus comprises engine rotational speed detecting means, fuel cut means, shift operation detecting means, timing means, and fuel cut prohibiting means. The engine rotational speed detecting means detects the rotational speed of the engine. The fuel cut means suppresses a rise in engine rotational speed by stopping the supply of fuel in a non-drive range if the rotational speed of the engine exceeds a predetermined set value with the shift lever having been shifted into the non-drive range. The shift operation detecting means detects movement of the shift lever from a drive range to a non-drive range. The timing means measures the time that has elapsed since detection of movement of the shift lever from a drive range to a non-drive range by the shift operation detecting means. The fuel cut prohibiting means prohibits the fuel cut means from stopping the supply of fuel if the elapsed time measured by the timing means exceeds a predetermined value.
In the control apparatus for a vehicular automatic transmission disclosed in HEI 5-141284, the timing means measures the time elapsed since movement of the shift lever from a drive range to a non-drive range is detected by the shift operation detecting means. If the elapsed time exceeds the predetermined value, the fuel cut prohibiting means prohibits the supply of fuel from being stopped in the non-drive range. Accordingly, the fuel cut means, for stopping the supply of fuel in the non-drive range if the speed of the engine exceeds the predetermined set value, restrains the hydraulically operated frictional engagement device from being dragged as a result of movement of the shift lever from the drive range to the non-drive range. In addition, if the elapsed time exceeds the predetermined value, the supply of fuel is prohibited from being stopped, so that the rotational speed of the engine can be raised above the predetermined set value in the non-drive range such as the P range or the N range. Therefore, it is possible to check the operation of the engine and to charge a battery. Further, since the engine racing, i.e., raising the rotational speed of the engine, is in the non-drive range, a driver is prevented from wrongly believing that the engine is malfunctioning.
However, the control apparatuses disclosed in the aforementioned two publications cannot solve a significant problem as follows. Before a predetermined period has elapsed after a shift of the automatic transmission from a drive position to a non-drive position, the increase in engine output is suppressed even if the accelerator pedal has been operated to increase output from the driving power source. Therefore, even if the driver depresses the accelerator pedal with the intention of increasing the RPM of the engine, the engine does not operate as intended by the driver and the driver thus feels a sense of incongruity.